35CL NQR STUDY ON TTF-CA CRYSTALS - SYMMETRY LOWERING AND HYSTERESIS AT THE NEUTRAL-TO-IONIC TRANSITION

Cl-35 NQR measurements were performed on a sample consisting of crysta ls of the mixed-stack charge transfer complex tetrathiafulvalene-p-chl oranil (TTF-CA) which were several millimetres in size. Under cooling, this compound undergoes the so-called neutral-to-ionic transition at T(N-1) congruent-to 80 K, which is responsible for important changes i n Cl-35 NQR spectra. The present study completes previous ones made on powdered TTF-CA and allows resolution of a small splitting on the hig hest intensity line in the ionic phase. Results are discussed in terms of symmetry lowering and are related to recent neutron diffraction st udies. Additionally, new features concerning hysteresis phenomena arou nd T(N-1) with a small coexistence area of about 3 K for both the neut ral and ionic species are presented.